Electrically insulating feed-through for cryogenic applications

ABSTRACT

An electrical connector suitable for cryogenic applications of virtually all metal construction employing anodized aluminum rings to provide electrical isolation.

United States Patent [191 Bamberger et a].

[ ELECTRICALLY INSULATING FEED-THROUGH FOR CRYOGENIC APPLICATIONS [451Sept. 9, 1975 2,616,946 11/1952 Scheer....- 174/151 3,352,963 ll/1967Homrig l74/18X FOREIGN PATENTS OR APPLICATIONS 1,161,606 1/1964 Germany174/152 R OTHER PUBLICATIONS (S2819 0044) Maznitsa, A. M., et al.,Low-Temperature Vacuum-Tight Current Input Lead, translated from Priboryi Tekhnika Eksperimenta, No. 1, p. 223, Jan.-Feb. 1972.

Primary Examiner-Laramie E. Askin Attorney, Agent, or Firm-Dean E.Carlson; Leonard Belkin An electrical connector suitable for cryogenicapplications of virtually all metal construction employing anodizedaluminum rings to provide electrical isolation.

ABSTRACT 9 Claims, 2 Drawing Figures Facing Surfaces Can/ed wifh E paxyor Anaerobic E. Sea/an! .iiiliilllllllll! Anodized Aluminum Rings 2 4244d(Thirk Anodized Aluminum Ring) 440 Fig.1

PATENTEUSEP Facing Surfaces Coated with Epoxy 0r Anaerobic AnodizedAluminum Rings 44d (Thick Anodized Aluminum Ring ELECTRICALLY INSULATINGFEED-THROUGH FOR CRYOGENIC APPLICATIONS BACKGROUND OF THE INVENTION Thisinvention was made in the course of, or under a contract with the UnitedStates Atomic Energy Commission.

Electrical connections to superconducting apparatus at cryogenictemperatures present problems which are unique and heretofore have beendifficult to overcome. Such connections must not only be capable ofproviding'adequate electrical insulation, but in addition the connectionmust frequently be leak tight over a period of time during numerousrecyclings between ambient and liquid helium temperatures and highpressures. Filament-wound fiberglass and epoxied connectors tosuperconducting magnets have been tried, but after several temperaturecycles, cryogen leaks into the insulating vacuum tend to develop throughcracks in the plastic connectors. In addition, because of the mechanicalstrength requirements in situations where a high current capacity isrequired, a completely metal configuration is desirable, but then theelectrical insulating properties are difficult to attain.

SUMMARY OF THE INVENTION The present invention overcomes the problemsmentioned above by providing an electrical connector of virtually allmetal parts capable of being leak tight to better than 5 X std. cc/secleak rate at a liquid helium temperature and pressure of atm and aboveand remaining tight after repeated temperature cycling from roomtemperature to liquid helium temperature. In addition, the connectordesigned in accordance with the principles of this invention is capableof withstanding repeated acceleration forces of 2 gs and carryingcurrents of 5,000 amperes and higher, including support of theinsulation housing and conductor required to carry such high currents.The connector has sufficiently high dielectric strength in thefeedthrough as to isolate the incoming and outgoing leads from eachother, and, also, to insulate the penetrating leads from associatedplumbing and dewars.

In accordance with a preferred embodiment of this invention there isprovided a first tubular member communicating at one end with theinterior of the dewars, a second tubular member aligned with the firstmember and closed at the opposite end, anodized aluminum ringscompressed between the open ends of the tubular members, and anelectrical conductor passing through while contacting the closed end ofthe second tubular member into the dewars without touching the innerwalls of the tubular members. In this arrangement, the interiors of thetubular members are open to the dewars, completely pressure sealed bythe rings and the closed end of the second tubular member. The secondtubular member is electrically isolated from the first tubular memberand the dewars by the anodized aluminum rings.

It is therefore a principal object of this invention to provide anelectrical feedthrough connector suitable for use under cryogenictemperature and pressure conditions.

Other objects and advantages of this invention will hereinafter becomeobvious from the following description of a preferred embodiment of thisinvention.

DESCRIPTION OF THE DRAWINGS;

FIG. 1 shows an elevation view in section of a preferred embodiment ofthis invention.

FIG. 2 shows an alternative preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

Referring to FIG. 1, electrical feedthrough connector 10 is providedwith an electrical conductor 12 to pass into dewars 14 which may be at apressure within which is substantially higher than the pressure outside.Typically conductor 12 would be one of the conductors to asuperconducting magnet (not shown) within dewars 14 and there would be asecond conductor (not shown) with its own connector (not shown) for thereturn electrical lead. Connector l0 and dewars 14 may be within anouter containment (not shown) so that there is a vacuum surroundingthese assemblies. Another connector would be employed to penetrate theouter containment. Conductor 12 may carry currents as high as 5,000amperes and above and the temperatures and pressures may be recycledperiodically to ambient conditions in order for access to be gained tothe equipment within dewars l4.

Connector 10 consists of a pair of tubular elements 16 and 18 axiallyaligned and a pair of housing members consisting of the male member 22threaded externally at 22a with a hexagonal lip 23 for gripping by awrench and the female member 24, threaded internally at 24a, the formermember being threaded into the latter, as is illustrated. A set screw 25is employed to prevent element 22 from unscrewing from element 24 whilein use.

Tubular element 16 at one end is welded or brazed to the wall of dewars14 with an opening 26 to match that of element 16 so that there iscommunication between the interior of dewars 14 with that of element 16.The other end of the latter terminates in an annular lip 28 for apurpose to be later described.

Tubular element 18 has at one end an annular lip 32 facing but spacedfrom lip 28 while the other end of element 18 is provided with a closurecap 34 which is welded or brazed to both element 18 and conductor 12 sothat there is complete sealing by all metallic parts.

Surrounding element 16 is a sleeve 36 of suitable electricallyinsulating deformable material such as Teflon, while surrounding element18 is a similar sleeve 38. A third sleeve 42 of similar materialencloses annular lips 28 and 32.

A plurality of anodized aluminum rings or washers 44a, 44b, and 44cproviding electrical insulation are mounted adjacent annular lips 28 and32 as is illustrated. Male housing member 22 is threaded into femalemember 24 to an extent to place washers 44a, 44b, and 44c undersufiicient compression and to insure as well proper confinement of thefluid within dewars l4 and tubular members 16 and 18. A thicker anodizedaluminum ring 44d may be employed in contact with male member 22. Atypical load on the washers with helium within dewars l4 and a vacuumoutside is 50,000 psi. By anodized aluminum is meant herein that theoxide layer on the metal is at least onehalf mil in thickness. So thatthe aforementioned washers 44b will provide leak tight confinement forthe fluid within connector 10, a sealant would be applied to the facingsurfaces of lips 28 and 32 and to the faces of washers 44b to effect theseal. Any suitable sealant may be applied for this purpose, such as acommercially available anaerobic sealant or an epoxy, so that thesealant will set up under compression.

Sleeves 36, 38 and 42 perform the function of providing electricalinsulation between members 22 and 24 on the one hand and tubular members16 and 18 on the other hand.

It will be seen that in the use of connector the latter simultaneouslyseals against leakage of fluid within dewars 14 through the use ofanodized aluminum rings 44b and that the anodized rings 44a, 44b, and44c isolate electrically conductor 12 and tubular member 18 from dewarsl4 and tubular member 16. That is, tubular member 18 is at the electricpotential of conductor 12 whereas dewars 14 and tubular member 16 are atsome other potential, i.e., neutral, ground, or opposite potential. Ofcourse, if desired, connector 10 may be utilized to perform either theelectrical isolation or the pressure containment alone as well as incombination.

In the arrangement illustrated in FIG. 1, connector 10 provides for thetransfer of electrical current into or out of dewars 14 as well as tightconfinement of the fluid within. Connector 10 may be so employed only topermit transfer of fluid into or out of dewars 14 while at the same timeelectrically isolating dewars 14 from the supply pipe. As shown in FIG.2, it is seen that in this configuration instead of a conductor 12,there is employed a transition member 52 terminating in a pipe 54 weldedor brazed to the end of tubular member 18. Gas flow is shown by thearrows which may be in either direction.

It will be seen that the electrical connector described herein is highlyuseful in cryogenic apparatus and systems, especially where temperaturecycling may take place. The construction is virtually all metal so thatthe destructive effects of temperature and/or pressure cycling areavoided. In addition, by selecting the metal of tubular elements 16 and18 to have a lower temperature coefficient of expansion than the metalselected for members 22 and 24, as the temperature is reduced, thepressure on rings 44a, 44b, and 440 is increased. In one typicalapplication stainless steel was employed for tubular elements 16 and 18while aluminum was employed for members 22 and 24.

What is claimed is:

1. An electrical connector for use with a dewars, comprising a. firstmetallic tubular means open at one end for communicating with a dewars:

b. second metallic tubular means aligned with and spaced from said firsttubular means closed at the end away from said first tubular means;

0. means consisting of stacked anodized aluminum washers, adjacentwashers being in contact with each other, filling the space between saidfirst and second tubular means;

d. means compressing said washers forming a sealed chamber within saidtubular means for communicating with the interior of a dewars, saidanodized aluminum washers electrically isolating said tubular means fromeach other; and

e. means extending through and in contact with the closed end of saidsecond tubular means, for providing communication with the interior ofsaid connector and a dewars.

2. The connector of claim 1 in which said tubular means are eachprovided with an annular lip at the open end facing each other, saidwashers filling the space between said lips.

3. The connector of claim 2 having additional anodized aluminum washerssurrounding said tubular means on the opposite sides of said annularlips, said compressing means compressing all of said washers.

4. The connector of claim 3 in which said compressing means comprises apair of threaded male and female members surrounding said tubular meansand enclosing said washers and compressing the latter, the male memberbeing threaded into the female member.

5. The connector of claim 4 having tubular sleeves of deformable,electrically insulating material separating said male and femalethreaded members from the annular lips and washers, and separating thethreaded members and the additional washers from the tubular means.

6. The connector of claim 4 in which the coefficient of thermalexpansion of said threaded members is greater than the coefficient ofthermal expansion of said tubular means.

7. The connector of claim 2 in which said washers and the annular lipsfacing said wahers are coated on contacting surfaces with sealant.

8. The connector of claim- 7 in which the means extending through and incontact with the closed end of said second tubular means consists of anelectrical conductor passing through both of said tubular means forextending into a dewars and spaced from the inner walls of both saidtubular means.

9. An electrical connector for use with a dewars, comprising a. firstmetallic tubular means open at one end for communication with a dewars;

b. second metallic tubular means aligned with and spaced from said firsttubular means closed at the end away from said first tubular means;

0. means consisting of stacked anodized aluminum washers, adjacentwashers being in contact with each other, filling the space between saidfirst and second tubular means; and

(1. means compressing said washers forming a sealed chamber within saidtubular means for communicating with the interior of a dewars, saidanodized aluminum washers electrically isolating said tubular means fromeach other;

e. said closed end of said second tubular means having an openingtherein for providing communication with the interior of said connectorand a dewars.

1. An electrical connector for use with a dewars, comprising a. firstmetallic tubular means open at one end for communicating with a dewars:b. second metallic tubular means aligned with and spaced from said firsttubular means closed at the end away from said first tubular means; c.means consisting of stacked anodized aluminum washers, adjacent washersbeing in contact with each other, filling the space between said firstand second tubular means; d. means compressing said washers forming asealed chamber within said tubular means for communicating with theinterior of a dewars, said anodized aluminum washers electricallyisolating said tubular means from each other; and e. means extendingthrough and in contact with the closed end of said second tubular means,for providing communication with the interior of said connector and adewars.
 2. The connector of claim 1 in which said tubular means are eachprovided with an annular lip at the open end facing each other, saidwashers filling the space between said lips.
 3. The connector of claim 2having additional anodized aluminum washers surrounding said tubularmeans on the opposite sides of said annular lips, said compressing meanscompressing all of said washers.
 4. The connector of claim 3 in whichsaid compressing means comprises a pair of threaded male and femalemembers surrounding said tubular means and enclosing said washers andcompressing the latter, the male member being threaded into the femalemember.
 5. The connector of claim 4 having tubular sleeves ofdeformable, electrically insulating material separating said male andfemale threaded members from the annular lips and washers, andseparating the threaded members and the additional washers from thetubular means.
 6. The connector of claim 4 in which the coefficient ofthermal expansion of said threaded members is greater than thecoefficient of thermal expansion of said tubular means.
 7. The connectorof claim 2 in which said washErs and the annular lips facing said wahersare coated on contacting surfaces with sealant.
 8. The connector ofclaim 7 in which the means extending through and in contact with theclosed end of said second tubular means consists of an electricalconductor passing through both of said tubular means for extending intoa dewars and spaced from the inner walls of both said tubular means. 9.An electrical connector for use with a dewars, comprising a. firstmetallic tubular means open at one end for communication with a dewars;b. second metallic tubular means aligned with and spaced from said firsttubular means closed at the end away from said first tubular means; c.means consisting of stacked anodized aluminum washers, adjacent washersbeing in contact with each other, filling the space between said firstand second tubular means; and d. means compressing said washers forminga sealed chamber within said tubular means for communicating with theinterior of a dewars, said anodized aluminum washers electricallyisolating said tubular means from each other; e. said closed end of saidsecond tubular means having an opening therein for providingcommunication with the interior of said connector and a dewars.